Let's see... I've never made a nuclear power plant from IC2 because I've never had any reason to, they've always looked to be far more trouble then they're worth. This changed in the 1.6 IC2 with their new mechanics (after watching some Direwolf videos), but by now I gave up on IC2 altogether so I don't think I'll make that reactor any time soon. Same for Quantum/Gravity suits, sure they're good but getting all that UU-matter is such a pain (even more so in the current version).
And I guess I've never bothered with Railcraft's rails either before dropping it.
I can't think of much else from popular mods or vanilla that I haven't tried yet, even some of the rarest things mentioned here (except for making a decent base, I suck horribly at that). I even tried IC2 crops once because I couldn't find cocoa beans anywhere to progress with Dartcraft (and oh boy I HATED IT SO MUCH. STOP GROWING WEED YOU)
And I guess I've never bothered with Railcraft's rails either before dropping it.
I can't think of much else from popular mods or vanilla that I haven't tried yet, even some of the rarest things mentioned here (except for making a decent base, I suck horribly at that). I even tried IC2 crops once because I couldn't find cocoa beans anywhere to progress with Dartcraft (and oh boy I HATED IT SO MUCH. STOP GROWING WEED YOU)